The present invention relates to a photoelectric smoke sensor and lighting equipment, as well as to a technique for achieving size reduction of the photoelectric smoke sensor and enhancement of its smoke sensibility.
In photoelectric smoke sensors intended for detection of smoke, dust and the like, there have conventionally been employed reflection- or transmission-type sensors or the like using an infrared LED (Light Emitting Diode) and a silicon photodiode. Varieties of contrivance have been incorporated in the placement of those light emitting/receiving elements or the housing internal structure to give thereto effects for removal of disturbance light and removal of stray light.
In one example of conventional photoelectric smoke sensors using a reflection-type sensor, with a view to reducing disturbance light that becomes incident on a light receiving element, a prism lens is used in front of an optical path of a light emitting element and the light receiving element to change the optical path so that the arrangement of the light receiving/emitting elements and the prism lens has a specified angle that prevents light from the light emitting element from going directly into the light receiving element (see, e.g., JP H9-231485 A).
In the housing of this photoelectric smoke sensor, a labyrinth structure is formed by providing therein a disturbance-light shielding pillar for light-trap purpose. This labyrinth structure of the housing is rough-surface processed internally so as to reduce the influences of disturbance light and stray light, thereby reducing characteristic variations due to temperature variations or other environmental variations. However, the optical path change by using a prism lens as described above involves the need for separating the optical path away from a housing bottom portion or cover portion in order to avoid any influences of reflected light inside the housing. This makes an obstacle to thinning of the housing as a problem, incurring limitations on the usage and place of use of the sensor. Besides, use of a larger housing or prism lens would obstruct cost reduction as another effect.
In an optical system in which the optical axis extends slantly upward, such as in conventional photoelectric sensors using diffuse reflected light, the housing, if present forward of the light emitting element, would cause the reflection inside the housing to be larger, necessitating widening the inside of the housing, which leads to a larger size of the sensor itself as a problem. However, without reduction in the internal reflection, disturbance light or internal reflected light other than the diffuse reflected light from smoke would go incident on the light receiving element, with the results of not only deterioration of smoke sensing precision but also vulnerability of the sensor to temperature changes and disturbance light or other surrounding environment changes. Further, use of a prism lens or other like optical parts and size increase of the housing would lead to cost increases.